A portable device developed for the space program to examine how physical activity relates to bone density may someday serve as a way to assess a person's risk of osteoporosis.

The device, developed by researchers in the Life Sciences Division at NASA's Ames Research Center, Moffett Field, CA, provides a record of the major forces people apply to their bodies throughout the day. It does this by measuring and recording the interaction between the foot and the ground during daily activity. This "loading" of the body plays an important role in maintaining muscle and bone strength in the lower limbs.

"This device was designed to quantify daily physical activity and daily musculoskeletal loading by measuring the ground-reaction force," said Dr. Robert Whalen, head of the Musculoskeletal Biomechanics Laboratory in the Gravitational Research Branch at Ames. The device measures the force that occurs on the foot during each step. The force can reach one and one-half times a person's body weight during walking and two to three times body weight during running. "It's very important to monitor this force throughout the day because it also is responsible for high muscle and bone forces in the legs and critical bone regions such as the hip and pelvis," Whalen explained.

The force exerted on the body when it meets the ground is what keeps muscles and bones in the lower body strong. If muscles and bones aren't used, they become significantly weaker, a problem encountered by astronauts during space flight, particularly by astronauts who do not exercise vigorously in space. "Maintaining muscles and bones during long duration space flight is primarily a biomechanical problem," Whalen said. "With current in-flight exercise devices, it is difficult to achieve force levels equivalent to levels achieved during normal daily activity on Earth. We are investigating new ways to counteract these changes with devices capable of imposing Earth-equivalent levels of force on the body in space."

Whalen and Dr. Gregory Breit, researchers at Ames, are studying the relationship between the mechanical forces humans put on the skeleton every day and the structure of the skeleton. "Bone is highly responsive to mechanical forces," Breit said. "That may be the key to understanding why bone is lost gradually with age and why certain exercise programs can't build bone mass," Whalen added.

The key, Whalen explained, is determining how individuals can "load" their bodies to maintain muscle and bone strength. Since our muscles generate their own forces, we are limited by how strong our muscles are. "If you don't have the muscle strength, you can't exert high forces on bones to increase bone mass," Whalen said. "As people age, a gradual decline in activity level and intensity contributes to a decline in muscle strength, and therefore our ability to load our bones also decreases." The result can be less dense, weaker bones that are more prone to fractures.

The device consists of two elements: a force sensor resembling an insole that is worn in the shoe, and a small computer carried in a fanny pack. A cable connects the sensor to the small computer, which samples the applied force 100 times per second. It stores only the significant maximum and minimum forces occurring during each loading or gait cycle, as well as the peak loading and unloading rate and the time at which each event occurred. The device is capable of storing approximately two weeks of activity data.

Although scientists have used step-meters and activity logs to estimate a person's daily activity level and musculoskeletal loading history, Whalen said these devices don't give a reliable measurement of forces on the skeleton, due to differences among people and differences in the amount and "intensity" of their daily activities. A person walking quickly will generally experience higher forces than when walking more slowly, for example. The new device provides a reliable measure of the actual forces exerted on the body.

The Ames researchers are collaborating with the Palo Alto Veterans Administration Hospital and with Stanford University, Palo Alto, CA, to study how daily activity level and exercise influence bone density. "Once we have enough data, we can get an idea of the daily physical activity level of an 'average' person," Breit said. "Then people can decide if they are above or below average and what they need to do to improve. In the future, we hope to understand bone adaptation well enough to assess whether an individual's bone density is consistent with his or her daily activity level."

Breit said that this device will allow measurement of an individual's activity to assess his or her risk of low bone density from low physical activity level and will allow an individual exercise prescription to improve the health of an older person.

For photographs or more information about the Musculoskeletal Biomechanics Laboratory, visit the Web site at URL:

National Aeronautics And Space Administration. "NASA Technology May Help Assess Risk Of Bone Problems." ScienceDaily. ScienceDaily, 22 July 1997. <www.sciencedaily.com/releases/1997/07/970722054403.htm>.

National Aeronautics And Space Administration. (1997, July 22). NASA Technology May Help Assess Risk Of Bone Problems. ScienceDaily. Retrieved August 2, 2015 from www.sciencedaily.com/releases/1997/07/970722054403.htm

National Aeronautics And Space Administration. "NASA Technology May Help Assess Risk Of Bone Problems." ScienceDaily. www.sciencedaily.com/releases/1997/07/970722054403.htm (accessed August 2, 2015).

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